In recent years, a number of liquid crystal display devices have been used in home televisions, computers, videophones, and the like. Many of these liquid crystal display devices have a backlight. Particularly, liquid crystal display devices used in the printing industry and for medical application require reproducibility, so that the light quantity of the backlight is controlled by providing photodetectors on back surfaces of the liquid crystal display devices and performing photometry on the light quantity of the backlight. Furthermore, in liquid crystal panels, light transmission characteristics undergo nonlinearly significant changes due to operating temperature and time deterioration. Hence, photometry from a front surface of the liquid crystal, as well as the light control of the backlight and the liquid crystal are performed these days, and its image sensors and photodetectors are often calibrated manually by putting moving sensors separated from the liquid crystal display devices closer to display screens, or often calibrated with sensors fixed by covering a part of the front surface of the liquid crystal.
However, if photometry of the light quantity on the front surface of the liquid crystal is performed with the moving sensors separated from the liquid crystal display devices in a conventional way, such photometry operation is demanding in a printing site or a medical site in which a lot of liquid crystal display devices are used in one place as has been the case in recent times, and inconvenient. On the other hand, if photometry is performed with the fixed sensors, display of a part of a screen is always sacrificed, with a problem that the whole screen cannot be effectively displayed. In addition, either method involves attempts to perform photometry on the light quantity of light from the backlight appearing on a front surface of the liquid crystal display device, but photometry in a bright room is affected by ambient light, and thus it does not always result in photometry of a correct light quantity. A photometry method and a calibration method with either problem solved are being desired.
Accordingly, an object of the present invention is to provide a photometric device of a liquid crystal display device which is capable of performing photometry without manpower, and which does not shield a liquid crystal surface other than during photometry, and the liquid crystal display device.